Latent heat storage material and method for manufacturing the same

ABSTRACT

A latent heat storage material includes a latent heat storage member formed of an organic compound, and a metallic seamless capsule encapsulating the latent heat storage member. A method for manufacturing the latent heat storage material includes preparing a grain of the latent heat storage member, supporting a powder on the latent heat storage member, conducting an electroless plating to form a first plating layer of the metallic seamless capsule on a surface of the latent heat storage member, and conducting an electrolytic plating to form a second plating layer of the metallic seamless capsule on a surface of the first plating layer.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2016-215745 filed on Nov. 3, 2016, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a latent heat storage material storing a heat by a solid-liquid phase transition and a method for manufacturing the latent heat storage material.

BACKGROUND

For example, a conventional latent heat storage material is exemplified by a latent heat storage capsule disclosed in JP H11-23172 A. The latent heat storage capsule includes a latent heat storage member and a metal coat covering a surface of the latent heat storage member. Since the metal coat covers the surface of the latent heat storage member, the latent heat storage material disclosed in JP H11-23172 A has relatively high mechanical strength.

SUMMARY

However, in the conventional latent heat storage material disclosed in JP H11-23172 A, the latent heat storage member is formed of a metal such as lead and has a relatively high solid-liquid phase transition temperature. Therefore, there is a possibility that the conventional latent heat storage material does not easily stores a waste heat in a low temperature range as a latent heat, the waste heat in the low temperature range being wasted in large amounts in industry. Furthermore, when the metal such as lead is employed as the latent heat storage member, there is a possibility that a weight of the latent heat storage material is extremely increased due to a relatively high specific gravity of the latent heat storage member.

It is an object of the present disclosure to provide a latent heat storage material that is light, mechanically strong, and capable of easily storing a waste heat in a low temperature range as a latent heat, and to provide a method for manufacturing the latent heat storage material.

According to a first aspect of the present disclosure, the latent heat storage material includes a latent heat storage member and a metallic seamless capsule. The latent heat storage member is formed of an organic compound. The metallic seamless capsule encapsulates the latent heat storage member.

According to the first aspect of the present disclosure, the metallic seamless capsule has no joint and has relatively high strength. Accordingly, the latent heat storage material is relatively light and mechanically strong, and the latent heat storage material easily stores the waste heat in the low temperature range as the latent heat.

According to a second aspect of the present disclosure, a method for manufacturing a latent heat storage material includes preparing a grain of a latent heat storage member formed of an organic compound, supporting a powder on the latent heat storage member, conducting an electroless plating, and conducting an electrolytic plating. In the supporting the powder, the powder formed of at least one of a metal and an oxide of the metal is pressed to a surface of the latent heat storage member prepared. In the conducting the electroless plating, a first plating layer is formed on the surface of the latent heat storage member by disposing a plating catalyst on the surface of the latent heat storage member and depositing the first plating layer from the powder and the plating catalyst as deposition starting points. In the conducting the electrolytic plating, a second plating layer is formed on a surface of the first plating layer after the conducting the electroless plating. The latent heat storage member is encapsulated in a metallic seamless capsule including the first plating layer and the second plating layer.

According to the second aspect of the present disclosure, the surface of the grain of the latent heat storage member prepared is easily covered by the first plating layer and the second plating layer formed in the electroless plating and the electrolytic plating. The powder is supported in addition to disposing the plating catalyst of the electroless plating. As a result, in the electroless plating, the first plating layer is formed to relatively uniformly cover the latent heat storage member and adhere tightly to the latent heat storage member.

In the electrolytic plating, the second plating layer deposits from the first plating layer and the thickness of the second plating layer is relatively easily controlled. Therefore, the capsule encapsulating the grain of the latent heat storage member formed of the organic compound is provided by the relatively strong metallic seamless capsule including the first plating layer and the second plating layer. Accordingly, the latent heat storage material that is relatively light, mechanically strong, and capable of easily storing the waste heat in the low temperature range as the latent heat is manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a cross-sectional view illustrating a schematic structure of a latent heat storage material according to a first embodiment;

FIG. 2 is a partial enlarged cross-sectional view of a portion II of the latent heat storage material of FIG. 1;

FIG. 3 is a cross-sectional view illustrating a schematic structure of the latent heat storage material when a latent heat storage member is in a liquid phase;

FIG. 4 is a cross-sectional view illustrating one example of a schematic structure of the latent heat storage material when the latent heat storage member is in a solid phase;

FIG. 5 is a flowchart diagram for explaining a method for manufacturing the latent heat storage material;

FIG. 6 is a diagram for explaining a grain forming step forming a grain of the latent heat storage member;

FIG. 7 is a cross-sectional view illustrating a schematic structure of the grain formed in the grain forming step;

FIG. 8 is a diagram for explaining a powder applying step applying a powder to a surface of the latent heat storage member;

FIG. 9 is a cross-sectional view schematically illustrating a structure of the latent heat storage member to which the powder is applied;

FIG. 10 is a diagram for explaining an electroless plating step; and

FIG. 11 is a cross-sectional view schematically illustrating a structure of the latent heat storage member covered by a first plating layer in the electroless plating step.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each embodiment, parts corresponding to parts described in preceding embodiment are designated by the same symbols and descriptions thereof will not be repeated. When only a part of configuration is described in the embodiment, the remaining part is similar to the preceding embodiment. The present disclosure is not limited to a combination specifically described in the embodiments and the embodiments may be partially combined as far as possible.

First Embodiment

A first embodiment of the present disclosure will be described with reference to FIG. 1 to FIG. 11.

As shown in FIG. 1, a latent heat storage material 1 of the present embodiment includes a latent heat storage member 10 and a metal coat 20. The latent heat storage member 10 is formed of an organic compound. The metal coat 20 is formed to accommodate the latent heat storage member 10 inside of the metal coat 20. For example, the latent heat storage material 1 is a granular material having a spherical outer shape and having an external diameter of about 4 millimeters (mm). The metal coat 20 is formed of a plating coat and does not have any joint part and the like. The metal coat 20 corresponds to a seamless capsule of the present embodiment.

For example, the latent heat storage material 1 exchanges a heat with a cooling water of an internal-combustion engine mounted to a vehicle. For example, a collectivity of multiple latent heat storage materials 1 is positioned at a circulation route of the cooling water. When a temperature of the cooling water is relatively high, the latent heat storage material 1 receives a waste heat from the cooling water and stores the waste heat as a latent heat by changing a phase from a solid phase to a liquid phase. When the temperature of the cooling water is relatively low, the latent heat storage material 1 releases the latent heat to the cooling water by changing the phase from the liquid phase to the solid phase.

For example, a main constituent of the latent heat storage member 10 is dotriacontane that is normal paraffin with 32 carbons. When dotriacontane is employed as the organic compound of the latent heat storage member 10, the latent heat storage member 10 has a melting point at 69 degrees Celsius (° C.). The latent heat storage member 10 has a solidifying point at 69° C. The latent heat storage member 10 has a phase transition temperature at 69° C., the liquid phase and the solid phase being capable of coexisting at the phase transition temperature. For example, the melting point and the solidifying point are defined based on JISK7121. For example, the latent heat storage member 10 of the present embodiment is provided from Paraffin Wax-155 manufactured by NIPPON SEIRO CO., LTD.

When the temperature of the cooling water flowing along an external surface of the latent heat storage material 1 is higher than the melting point of the latent heat storage member 10, the latent heat storage member 10 receives the heat from the cooling water through the metal coat 20 and the latent heat storage member 10 is melted. When the temperature of the cooling water flowing along the external surface of the latent heat storage material 1 is lower than the melting point of the latent heat storage member 10, the latent heat storage member 10 is solidified and releases the heat to the cooling water through the metal coat 20.

The organic compound of the latent heat storage member 10 is not limited to dotriacontane. Preferably, the organic compound of the latent heat storage member 10 has a melting point from 40° C. to 90° C. For example, a preferable temperature range defined by a thermal efficiency of the internal-combustion engine has a lower limit at 40° C. and an upper limit at 90° C. For example, when the internal-combustion engine is mounted to the vehicle, the temperature of the cooling water after warming is finished is set at 40° C. For example, the temperature of the cooling water in a general stationary driving mode is set at 90° C. When the organic compound of the latent heat storage member 10 has a melting point from 40° C. to 90° C., the waste heat of the cooling water in the stationary driving mode is stored in the latent heat storage member 10 and the waste heat is employed for warming when the internal-combustion engine is restarted.

As the organic compound of the latent heat storage member 10, normal paraffin with 21 to 46 carbons may be employed. Henicosane, which is normal paraffin with 21 carbons, has a melting point at 40.5° C. Hexatetracontane, which is normal paraffin with 46 carbons, has a melting point from 86° C. to 89° C. The phase transition temperature of the latent heat storage member 10 is set from 40° C. to 90° C. by employing normal paraffin with 21 to 46 carbons solely or by mixture.

One example is described in which the external diameter of the latent heat storage material 1, that is, the external diameter of the metal coat 20 is about 4 mm. However, the external diameter of the latent heat storage material 1 is preferably from 1 mm to 10 mm. When the external diameter of the latent heat storage material 1 is less than 1 mm, the latent heat storage material 1 is a fine powder and is relatively difficult to be handled. When the external diameter of the latent heat storage material 1 is greater than 10 mm, the latent heat storage material 1 has smaller specific surface area and has less efficiency of exchanging the heat with the cooling water. Accordingly, the external diameter of the latent heat storage material 1 is preferably from 1 mm to 10 mm. The external diameter of the latent heat storage material 1 is more preferably from 2 mm to 7 mm, and further preferably from 2.5 mm to 5 mm.

For example, the metal coat 20 is made of copper. That is, the metal coat 20 is formed of a copper plating film. For example, an average thickness t of the metal coat 20 is 50 micrometers (μm). Therefore, in the present embodiment, the average thickness t of the metal coat 20 is about 1.25 percent (%) of the external diameter of the metal coat 20. The average thickness t of the metal coat 20 is preferably from 0.7% to 10% of the external diameter of the metal coat 20. When the average thickness t of the metal coat 20 is less than 0.7% of the external diameter of the metal coat 20, it is difficult to secure the mechanical strength of the metal coat 20. When the average thickness t of the metal coat 20 is greater than 10% of the external diameter of the metal coat 20, a volume ratio of the metal coat 20 to the latent heat storage member 10 is increased over a preferable value. Accordingly, the average thickness t of the metal coat 20 is preferably from 0.7% to 10% of the external diameter of the metal coat 20. The average thickness t of the metal coat 20 is more preferably from 1% to 4% of the external diameter of the metal coat 20.

As shown in FIG. 2, the thickness of the metal coat 20 is slightly varied depending on positions along a direction in which the surface of the metal coat 20 extends. The variation in the thickness of the metal coat 20 is preferably ±30% of the average thickness t. In other words, the variation in the thickness of the metal coat 20 is preferably from −30% to +30% of the average thickness t. When the variation of the thickness of the metal coat 20 is out of the range of ±30% of average thickness t, the metal coat 20 is likely to be buckled or fractured by an increase of a difference between internal and external pressure. Accordingly, the variation of the thickness of the metal coat 20 is preferably from −30% to +30% of the average thickness t. The variation of the thickness of the metal coat 20 is more preferably from −25% to +25% of the average thickness t.

As shown by the range of the average thickness t in FIG. 2, the thickness of the metal coat 20 does not include a dimension of a protruding portion in which an inner surface of the metal coat 20 protrudes towards the latent heat storage member 10. The protruding portion of the metal coat 20 is caused by a powder 30 employed in manufacturing the latent heat storage material 1, which will be described later. The above described preferable average thickness t and variation of the metal coat 20 is based on the dimension not including the protruding portion.

As shown in FIG. 1, the latent heat storage material 1 has a cavity 11 inside of the metal coat 20. The latent heat storage member 10 in the solid phase does not exist in the cavity 11. That is, when the latent heat storage member 10 is in the solid phase, the latent heat storage member 10 occupies a part of an inner space of the metal coat 20 and defines the cavity 11 in a remaining part of the inner space. Inside of the cavity 11 is preferably vacuum. A small amount of gas may exist inside of the cavity 11. The cavity 11 is capable of accepting an increase of the volume of the latent heat storage member 10 when the phase of the latent heat storage member 10 is changed from the solid phase to the liquid phase. Accordingly, the cavity 11 preferably has a volume equal to or greater than the difference between a volume of the latent heat storage member 10 in the liquid phase and a volume of the latent heat storage member 10 in the solid phase.

The latent heat storage material 1 shown in FIG. 1 has the latent heat storage member 10 in the solid phase. When the latent heat storage member 10 receives the heat from the cooling water as the heat transferring medium flowing out of the latent heat storage material 1, the latent heat storage member 10 changes the phase to the liquid phase. In this case, for example as shown in FIG. 3, the cavity 11 disappears. When the volume of the cavity 11 shown in FIG. 1 is greater than the increase of the volume of the latent heat storage member 10 caused by the phase transition, the cavity 11 shrinks but does not disappear. When the latent heat storage member 10 releases the heat to the cooling water flowing out of the latent heat storage material 1, the latent heat storage member 10 changes the phase to the solid phase again. In this case, for example as shown in FIG. 4, the cavity 11 is generated between the latent heat storage member 10 and the metal coat 20. The cavity 11 generated when the latent heat storage member 10 is in the solid phase may be generated to be surrounded by the latent heat storage member 10, or may be generated between the latent heat storage member 10 and the metal coat 20.

Next, a method for manufacturing the latent heat storage material 1 having the above described configurations will be described. As shown in FIG. 5, in the method for manufacturing the latent heat storage material 1, a grain forming step 110, a powder applying step 120, an electroless plating step 130, an electrolytic plating step 140 are conducted in series.

As shown in FIG. 6, in the grain forming step 110, a droplet 10A of the melted latent heat storage member 10 in the liquid phase is dropped from a head of a nozzle 90 into cooling water 91 as a cooling liquid stored in a cooling bath 92. The cooling liquid is preferably a liquid that does not have compatibility with the organic compound of the latent heat storage member 10. In the present embodiment, the latent heat storage member 10 is water-insoluble normal paraffin and the cooling liquid is the cooling water 91. The droplet 10A dropped in the cooling water 91 is cooled by the cooling water 91 from outside and is solidified to form the grain of the latent heat storage member 10. The droplet 10A is gradually solidified from outside. As a result, as shown in FIG. 7, the latent heat storage member 10 in the solid phase has the cavity 11 at the center and the cavity 11 has the volume corresponding to several % of decrease of the volume caused by the phase transition.

The grain forming step 110 is a step for forming the grain of the latent heat storage member 10 shown in FIG. 7 by the method shown in FIG. 6. The grain forming step 110 is not limited to a step in which the droplet 10A of the latent heat storage member 10 is dropped into the cooling water 91. For example, the nozzle 90 may be placed so that the head of the nozzle 90 is located in the cooling water 91 and the droplet 10A may be supplied in the cooling water 91. The position of the nozzle 90 is not limited to the illustrated example. The droplet 10A may be supplied in the cooling water 91 from a side or a bottom of the cooling bath 92.

In the present embodiment, the grain forming step 110 corresponds to a preparing step preparing the grain of the latent heat storage member 10 including the organic compound. The preparing step is not limited to the grain forming step 110. The preparing step may be a step preparing the latent heat storage member 10 shown in, for example, FIG. 7 and supplying the latent heat storage member 10 to the latter steps.

As shown in FIG. 8, in the powder applying step 120, the grain of the latent heat storage member 10 formed in the grain forming step 110 and a powder 30 are put in a container 93 and the powder 30 is applied on a surface of the latent heat storage member 10. In the powder applying step 120, the powder 30 is pressed to the surface of the latent heat storage member 10 with a force causing a plastic deformation of the surface of the latent heat storage member 10. As such, the powder 30 is supported on the latent heat storage member 10 as shown in FIG. 9.

For example, when a glass container is employed as the container 93, the latent heat storage member 10 and the powder 30 are mixed in the container 93 rotated. In this case, the powder 30 is pressed to the latent heat storage member 10 by the rotation mixing and the powder 30 is supported on the latent heat storage member 10. For example, when a polyethylene bag is employed as the container 93, the latent heat storage member 10 and the powder 30 are mixed in the bag. In this case, the powder 30 is pressed to the latent heat storage member 10 by an external force depressing the bag and the powder is supported on the latent heat storage member 10.

The powder 30 includes at least one of a metal powder formed of copper and a metal oxide powder formed of copper oxide. In the present embodiment, the powder 30 is a copper oxide powder having a cubic shape. An average diameter of the powder 30 is about 10 μm. A diameter of the powder 30 is preferably from 1 μm to 100 μm. When the diameter of the powder 30 is in such a range, a plating layer is stably formed in the subsequent electroless plating step 130. In the present embodiment, the powder 30 is the copper oxide powder whose distribution range of the diameter is from 1 μm to 20 μm and the average diameter is about 10 The powder 30 is preferably a particle having an average diameter less than the average thickness t of the metal coat 20 of the latent heat storage material 1 and having a polyhedron shape. When the average diameter of the powder 30 is less than the average thickness t of the metal coat 20, the increase of the variation in the thickness of the metal coat 20 is restricted in forming the metal coat 20. When the powder 30 has the polyhedron shape, a stress generated when the powder 30 is pressed to the latent heat storage member 10 is focused at corners and the powder 30 is surely supported on the latent heat storage member 10. For example, the diameter of the polyhedron shape including the cubic shape is a diagonal diameter having the maximum diameter.

In the present embodiment, the powder applying step 120 corresponds to a powder supporting step supporting the powder 30 formed of the metal or the oxide of the metal on the latent heat storage member 10 by pressing the powder to the surface of the latent heat storage member 10.

As shown in FIG. 5, after the powder applying step 120 is finished, the electroless plating step 130 is conducted. The electroless plating step 130 includes a catalyst disposing step 131, a water washing step 132, a catalyst activating step 133, a water washing step 134, an electroless copper plating step 135 and a water washing and drying step 136. In the electroless plating step 130, the above described steps are conducted in the above described order.

In the catalyst disposing step 131, a plating catalyst is disposed on the surface of the latent heat storage member 10 by using a catalyst solution. For example, the catalyst solution is a mixed solution of stannous chloride and paradigm chloride. The latent heat storage member 10 having the powder 30 supported is soaked in a paradigm-tin mixed colloid solution to dispose the plating catalyst to on the surface. There is a possibility that a part of the powder 30 supported on the surface of the mem in the powder applying step 120 is departed from the surface of the latent heat storage member 10 before the catalyst disposing step 131. In the powder applying step 120, the powder 30 is dogged in the latent heat storage member 10 and causes a plastic deformation. When the powder 30 dug in the latent heat storage member 10 is departed, a recess is formed in the latent heat storage member 10 at a position corresponding to the departed powder 30. Even though the powder 30 is departed from the latent heat storage member 10, in the catalyst disposing step 131, the catalyst is surely disposed on the latent heat storage member 10 using the recess.

After the catalyst disposing step 131 is conducted, the water washing step 132 and then the catalyst activating step 133 are conducted. For example, in the catalyst activating step 133, an acceleration treatment is conducted to remove the tin in the palladium-tin colloid and expose the metal palladium. The acceleration treatment is an acid treatment to soak the latent heat storage member 10 in an acid solution such as dilute hydrochloric acid or dilute sulfuric acid.

After the catalyst activating step 133 is conducted, the water washing step 134 and then the electroless copper plating step 135 are conducted. For example, in the electroless copper plating step 135, a barrel plating apparatus shown in FIG. 10 is employed. For example, the barrel plating apparatus includes a plating bath 94 and a barrel 96. The plating bath 94 stores a plating liquid 95 inside. The barrel 96 is a porous material and rotatable. The copper plating is formed on the surface of the latent heat storage member 10 in the barrel 96.

The average density of the latent heat storage member 10 is less than the average density of the plating liquid 95. That is, the latent heat storage member 10 is likely to emerge to a liquid surface 95 a in the plating liquid 95. In the present embodiment, multiple grains of the latent heat storage member 10 are put in a mesh bag 97 made of, for example, polyvinylidene chloride and the mesh bag 97 is put in the barrel 96. As such, the emergence of the latent heat storage member 10 is restricted, that is, the latent heat storage member 10 is restricted from being exposed upward from the liquid surface 95 a of the plating liquid 95. The mesh bag 97 holds down the latent heat storage member 10 so that the entirety of the latent heat storage member 10 is positioned below the liquid surface 95 a of the plating liquid 95. The mesh bag 97 has a fine mesh smaller than the diameter of the latent heat storage member 10. Therefore, the latent heat storage member 10 does not flow away from the relatively large holes of the barrel 96.

In the electroless copper plating step 135, a first plating layer 21, which is a copper plating film, is formed as shown in FIG. 11. The formation of the first plating layer 21 begins to deposit from the powder 30 supported on the latent heat storage member 10 and from the palladium catalyst disposed on the surface of the latent heat storage member 10 as deposition starting points. In the electroless copper plating step 135, the copper oxide of the powder 30 is reduced and functions as the deposition starting point of the electroless plating. After the electroless copper plating step 135 is conducted, the water washing and drying step 136 is conducted.

In the electroless plating step 130, an ambient temperature of the latent heat storage member 10 is kept lower than the melting point of the materials of the latent heat storage member 10 from the catalyst disposing step 131 to the water washing and drying step 136. When the organic compound of the latent heat storage member 10 is dotriacontane as in the present embodiment, the latent heat storage member 10 has the melting point at 69° C. In the present embodiment, the liquid temperature in the catalyst disposing step 131 is 30° C. The liquid temperature in the catalyst activating step 133 is around room temperature, which is a normal temperature. The liquid temperature of the plating liquid in the electroless copper plating step 135 is 33° C. Accordingly, in the electroless plating step 130, the first plating layer 21 is formed without breaking the grain shape of the latent heat storage member 10.

By the electroless plating step 130, the first plating layer 21 having a thickness of, for example, about 1 μm is formed on the entire surface of the latent heat storage member 10. The thickness of the first plating layer 21 is preferably from 0.5 μm to 2 μm.

As shown in FIG. 5, after the electroless plating step 130 is finished, the electrolytic plating step 140 is conducted. The electrolytic plating step 140 includes an acid activating step 141, a water washing step 142, an electrolytic copper plating step 143 and a water washing and drying step 144, In the electrolytic plating step 140, the above described steps are conducted in the above described order.

In the acid activating step 141, an activating treatment of the surface of the first plating layer 21 is conducted by using an acid solution such as dilute sulfuric acid. After the acid activating step 141 is conducted, the water washing step 142 and then the electrolytic copper plating step 143 are conducted. For example, in the electrolytic copper plating step 143, the barrel plating apparatus is employed similarly to the electroless copper plating step 135. In the barrel plating apparatus, a copper plating layer is further formed on the surface of the first plating layer 21 covering the entire surface of the latent heat storage member 10. For example, in the electrolytic copper plating step 143, the electrolytic copper plating is conducted to deposit the copper on the surface of the first plating layer 21 of the latent heat storage member 10 by using the pyrophosphotic acid copper plating liquid. For example, in the electrolytic copper plating step 143, 4A of current is energized.

Also in the electrolytic copper plating step 143, the average density of the latent heat storage member 10 including the first plating layer 21 is less than the average density of the plating liquid. That is, the latent heat storage member 10 including the first plating layer 21 is likely to emerge to a liquid surface in the plating liquid. In the present embodiment, also in the electrolytic copper plating step 143, similarly to the electroless copper plating step 135, multiple grains of the latent heat storage member 10 are put in a mesh bag made of, for example, polyvinylidene chloride and the mesh bag is put in the barrel. As such, the emergence of the latent heat storage member 10 is restricted, that is, the latent heat storage member 10 is restricted from being exposed upward from the liquid surface of the plating liquid. The mesh bag holds down the latent heat storage member 10 so that the entirety of the first plating layer 21 is positioned below the liquid surface of the plating liquid. The mesh bag has a fine mesh smaller than the diameter of the latent heat storage member 10. Therefore, the latent heat storage member 10 does not flow away from the relatively large holes of the barrel.

In the electrolytic copper plating step 143, a second plating layer 22, which is a copper plating film, is formed as shown in FIG. 2. The formation of the second plating layer 22 begins to deposit from the first plating layer 21 covering the entire surface of the latent heat storage member 10 as the deposition starting point. For example, the thickness of the second plating layer 22 is 50 μm. The metal coat 20 including the first plating layer 21 and the second plating layer 22 is formed by forming the second plating layer 22 over the first plating layer 21, After the electrolytic copper plating step 143 is conducted, the water washing and drying step 144 is conducted.

In the electrolytic plating step 140, the ambient temperature of the latent heat storage member 10 is kept lower than the melting point of the materials of the latent heat storage member 10 from the acid activating step 141 to the water washing and drying step 144. When the organic compound of the latent heat storage member 10 is dotoriacontane as in the present embodiment, the latent heat storage member 10 has the melting point at 69° C. In the present embodiment, the liquid temperature in the acid activating step 141 is around a room temperature, which is a normal temperature. The liquid temperature of the plating liquid in the electrolytic copper plating step 143 is 55° C. As such, in the electrolytic plating step 140, the second plating layer 22 is formed without breaking the grain shape of the latent heat storage member 10 covered by the first plating layer 21.

According to the above described latent heat storage material 1, the following effects are achieved.

The latent heat storage material 1 includes the latent heat storage member 10 formed of the organic compound and the metal coat 20 as the metallic seamless capsule encapsulating the latent heat storage member 10. The latent heat storage member 10 is formed of the organic compound having relatively small specific gravity and relatively low melting point. The metal coat 20 is the metallic seamless capsule having no joint and having relatively high strength. Accordingly, the latent heat storage material 1 is relatively light and mechanically strong, and the latent heat storage material 1 easily stores the waste heat in the low temperature range as the latent heat.

When the latent heat storage material 1 is mounted to the vehicle as in the present embodiment, the light latent heat storage material 1 is efficient in views of a vehicle weight and a loading capability. Since the latent heat storage material 1 is light and mechanically strong, the structure of the latent heat storage material 1 is likely to be sustained in a vehicular environment in which relatively large vibrations are likely to be applied. The internal-combustion engine mounted to the vehicle repeats operation and suspension, and a quantity of heat released from the internal-combustion engine to the cooling water largely varies with time. In this case, the latent heat storage material 1 easily keeps the temperature of the cooling water in a specific temperature range by the phase transition of the latent heat storage member 10.

The phase transition of the latent heat storage member 10 is frequently repeated and the stress caused by the internal and external pressure difference of the metal coat 20 is repeatedly applied to the metal coat 20. In this case, the seamless metal coat 20 has a tolerance. In a comparative example in which a metal coat is formed of a metal grain such as lead, when the metal grain changes the phase to the liquid phase, an expansion pressure is applied. When the solid-liquid phase transition is repeated, there is a possibility of the metal coat being broken. According to the latent heat storage material 1 of the present embodiment, the above described possibility is less likely to occur and high durability is secured.

The external diameter of the metal coat 20 is from 1 mm to 10 mm. Since the external diameter of the metal coat 20 is equal to or less than 10 mm the specific surface area of the latent heat storage material 1 is relatively large. In this case, the heat is easily transferred between the latent heat storage member 10 inside of the metal coat 20 and the heat transferring medium out of the metal coat 20. Since the external diameter of the metal coat 20 is equal to or greater than 1 mm, the latent heat storage material 1 is easily handled and is highly manufacturable.

The organic compound of the latent heat storage member 10 has the melting point from 40° C. to 90° C. As a result, the latent heat storage material 1 easily stores the waste heat in relatively low temperature range equal to or higher than the phase transition temperature, which is the melting and solidifying temperature. The latent heat storage material 1 releases the heat at the relatively low phase transition temperature.

The organic compound of the latent heat storage member 10 is normal paraffin with 21 to 46 carbons. For example, henicosane, which is normal paraffin with 21 carbons, has a melting point at 40.5° C. Hexatetracontane, which is normal paraffin with 46 carbons, has a melting point from 86° C. to 89° C. Therefore, the latent heat storage material 1 easily stores the waste heat in relatively low temperature range equal to or higher than the phase transition temperature, which is the melting/solidifying temperature. The latent heat storage material 1 releases the heat at the relatively low phase transition temperature.

When the latent heat storage member 10 is in the solid phase, the latent heat storage member 10 occupies a part of the inner space of the metal coat 20 and defines the cavity 11 in the remaining part of the inner space. The cavity 11 accepts the increase of the volume of the latent heat storage member 10 when the phase of the latent heat storage member 10 is changed from the solid phase to the liquid phase. Accordingly, the increase of the inner pressure caused by the phase transition from the solid phase to the liquid phase is restricted.

The volume of the cavity 11 is equal to or greater than the difference of the volume of the latent heat storage member 10 in the liquid phase and the volume of the latent heat storage member 10 in the solid phase. As a result, the cavity 11 surely accepts the increase of the volume of the latent heat storage member 10 caused by the phase transition from the solid phase to the liquid phase. Accordingly, the increase of the inner pressure caused by the phase transition from the solid phase to the liquid phase is surely restricted.

The metal coat 20 is made of copper. Therefore, the metal coat 20 is the relatively cheap seamless capsule having high heat conductivity.

The average thickness of the metal coat 20 is from 0.7% to 10% of the external diameter of the metal coat 20. As a result, the volume ratio of the metal coat 20 to the latent heat storage member 10 is reduced while securing the mechanical strength of the latent heat storage material 1. Accordingly, the heat is effectively transferred while reducing the weight of the latent heat storage material 1. Also, the metal coat 20 is easily manufacturable.

The variation of the thickness of the metal coat 20 is ±30% of the average thickness t. Even when the internal and external pressure difference of the metal coat 20 is large, the metal coat 20 is less likely to be buckled or fractured.

According to the above described method for manufacturing the latent heat storage material 1, the following effects are achieved.

The method for manufacturing the latent heat storage material 1 includes the grain forming step 110 as the preparing step, the powder applying step 120 as the powder supporting step, the electroless plating step 130 and the electrolytic plating step 140. In the preparing step, the grain of the latent heat storage member 10 formed of the organic compound is prepared. In the powder supporting step, the powder 30 including the metal powder or the metal oxide powder is supported on the latent heat storage member 10 by pressing the powder 30 to the surface of the latent heat storage member 10 prepared in the preparing step. In the electroless plating step 130, the electroless plating is conducted to form the first plating layer 21 on the surface of the latent heat storage member 10 by disposing the plating catalyst on the surface of the latent heat storage member 10 and depositing the first plating layer 21 from the powder 30 and the plating catalyst as the deposition starting points. In the electrolytic plating step 140, the electrolytic plating is conducted after the electroless plating step 130 to form the second plating layer 22 on the surface of the first plating layer 21. As a result of these steps, the latent heat storage material 1 in which the latent heat storage member 10 is encapsulated in the metal coat 20 including the first plating layer 21 and the second plating layer 22 is manufactured.

According to the method, the surface of the grain of the latent heat storage member 10, which is prepared in the preparing step, is easily covered by the first plating layer 21 and the second plating layer 22, which are formed in the electroless plating step 130 and the electrolytic plating step 140. The powder supporting step is conducted in addition to disposing the plating catalyst of the electroless plating. As a result, in the electroless plating step 130, the first plating layer 21 is formed to relatively uniformly cover the latent heat storage member 10 and adhere tightly to the latent heat storage member 10. In the electrolytic plating step 140, the second plating layer 22 deposits from the first plating layer 21 and the thickness of the second plating layer 22 is relatively easily controlled. Therefore, the capsule encapsulating the grain of the latent heal storage member 10 formed of the organic compound is provided by the relatively strong metallic seamless capsule including the first plating layer 21 and the second plating layer 22. Accordingly, the latent heat storage material 1 being relatively light, mechanically strong, and capable of easily storing the waste heat in the low temperature range as the latent heat is manufactured.

In the powder supporting step, the powder 30 includes at least one of the metal powder formed of the same metal as the first plating layer 21 and the metal oxide powder formed of the oxide of the same metal as the first plating layer. As a result, in the electroless plating step 130, the first plating layer 21 easily deposits from the catalyst and the powder 30 as the deposition starting points.

In the powder supporting step, the powder 30 has the diameter from 1 μm to 100 μm. As a result, in the powder supporting step, the powder 30 is easily supported on the latent heat storage member 10 and, in the electroless plating step 130, the first plating layer 21 is stably formed.

In the electroless plating step 130, the latent heat storage member 10 is held down so that the entirety of the latent heat storage member 10 is positioned below the liquid surface 95 a of the plating liquid 95. As a result, even when the mean density of the grain of the latent heat storage member 10 is less than the density of the plating liquid 95 of the electroless plating step 130, the first plating layer 21 is stably formed on the entire surface of the latent heat storage member 10.

In the electrolytic plating step 140, the latent heat storage member 10 having the first plating layer 21 on the surface is held down so that the entirety of the first plating layer 21 is positioned below the liquid surface of the plating liquid. As a result, even when the mean density of the latent heat storage member 10 having the first plating layer 21 is less than the density of the plating liquid of the electrolytic plating step 140, the second plating layer 22 is stably formed on the entire external surface of the first plating layer 21.

In the preparing step, the grain of the latent heat storage member 10 is formed by supplying the droplet 10A of the latent heat storage member 10 in the cooling water 91 as the cooling liquid, and solidifying the droplet 10A from outside. As a result, the latent heat storage member 10 in the liquid phase is gradually solidified from outside to form the grain of the latent heat storage member 10. Therefore, the latent heat storage member 10 having the cavity 11 inside is easily formed.

Other Embodiment

In the above embodiment, the organic compound of the latent heat storage member 10 is normal paraffin. However, the organic compound is not limited to normal paraffin. For example, isoparaffin or other organic compounds may be employed. The organic compound having the phase transition temperature corresponding to the relatively low temperature of the waste heat generated in industry, e.g., 40° C. to 200° C., is employed.

In the above embodiment, the metal of the metal coat 20 is Cu having high heat conductivity and being relatively cheap. However, the metal of the metal coat 20 is not limited to Cu. Metal capable of developing a self-catalytic electroless reaction, such as Cu, Ni, Co, Au, Ag, Pd, Rh, Pt, In and Sn may be employed. From viewpoints of heat conductivity, Cu, Au and Ag are preferable. From viewpoints of cost, Cu is most preferable.

The average thickness t of the metal coat 20 preferably satisfies the following formula (1), regardless of species of the metal.

2E/(3(1−v ²))^((1/2))(t/R)²<101.3 kPa  (1)

In the formula (1), E represents Young's modulus of the metal coat 20, v represents Poisson ratio of the metal coat 20, and R represents radius of the metal coat 20.

In the above embodiment, the powder 30 is at least one of the copper powder or the copper oxide powder. However, the powder 30 is not limited to the example. The powder 30 functions as the deposition starting point of the first plating layer 21. Therefore, the powder 30 preferably includes the metal powder formed of the same the metal or the metal oxide powder formed of the oxide of the same metal as the metal forming the first plating layer 21.

In the above embodiment, the powder 30 has the polyhedron shape. However, the shape of the powder 30 is not limited to the example. For example, the powder 30 may have a spherical shape. For example, the powder 30 may have an indefinite shape.

In the above embodiment, as the catalyst treatment before the plating of the electroless plating step 130, the catalyst-accelerator method is employed to remove tin in the palladium-tin colloid and expose metal palladium. However, the catalyst treatment is not limited to the example. For example, a sensitizer-activator method may be employed. For example, an alkali-ion-catalyst method may be employed.

In the above embodiment, the catalyst disposing step 131 of the electroless plating step 130 is conducted after the powder applying step 120. However, the order of steps is not limited to the example. For example, the powder 30 may be supported after the plating catalyst is disposed on the latent heat storage member 10. The plating metal at least deposits from the powder 30 and the plating catalyst in the electroless plating.

In the electroless copper plating step 135 and the electrolytic copper plating step 143 of the above embodiment, the entirety of the latent heat storage member 10 is positioned below the liquid surface of the plating liquid by using the mesh bag. However, the latent heat storage member 10 may be held down below the liquid surface by a member other than the mesh bag. The member holding down the latent heat storage member 10 may be employed in the step other than the electroless copper plating step 135 and the electrolytic copper plating step 143.

In the above embodiment, the latent heat storage material 1 exchanges heat with the cooling water of the internal-combustion engine mounted to the vehicle. However, the latent heat storage material 1 may exchange heat with other heat transferring medium employed in the industry. The present disclosure is effective for employing the relatively low waste heat wasted in the industry, e.g., 40° C. to 200° C.

While only the selected exemplary embodiment and examples have been chosen to illustrate the present disclosure, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the disclosure as defined in the appended claims. Furthermore, the foregoing description of the exemplary embodiment and examples according to the present disclosure is provided for illustration only, and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A latent heat storage material comprising: a latent heat storage member formed of an organic compound; and a metallic seamless capsule encapsulating the latent heat storage member.
 2. The latent heat storage material according to claim 1, wherein the metallic seamless capsule has an external diameter from 1 millimeter to 10 millimeters.
 3. The latent heat storage material according to claim 1, wherein the organic compound has a melting point from 40 degrees Celsius to 90 degrees Celsius.
 4. The latent heat storage material according to claim 1, wherein the organic compound includes normal paraffin with 21 to 46 carbons.
 5. The latent heat storage material according to claim 1, wherein when the latent heat storage member is in a solid phase, the latent heat storage member occupies a part of an inner space of the metallic seamless capsule and defines a cavity in a remaining part of the inner space.
 6. The latent heat storage material according to claim 5, wherein the cavity has a volume equal to or greater than a difference between a volume of the latent heat storage member in a liquid phase and a volume of the latent heat storage member in the solid phase.
 7. The latent heat storage material according to claim 1, wherein the metallic seamless capsule is made of copper.
 8. The latent heat storage material according to claim 7, wherein the metallic seamless capsule has an average thickness from 0.7 percent to 10 percent of an external diameter of the metallic seamless capsule.
 9. The latent heat storage material according to claim 8, wherein the metallic seamless capsule has a variation in a thickness from minus 30 percent to plus 30 percent of the average thickness of the metallic seamless capsule.
 10. A method for manufacturing a latent heat storage material, the method comprising: preparing a grain of a latent heat storage member formed of an organic compound; supporting a powder on the latent heat storage member by pressing the powder to a surface of the latent heat storage member prepared, the powder including at least one of a metal powder formed of a metal and a metal oxide powder formed of an oxide of the metal; conducting an electroless plating to form a first plating layer on the surface of the latent heat storage member by disposing a plating catalyst on the surface of the latent heat storage member and depositing the first plating layer from the powder and the plating catalyst as deposition starting points; and conducting an electrolytic plating to form a second plating layer on a surface of the first plating layer, after the conducting the electroless plating, wherein the latent heat storage member is encapsulated in a metallic seamless capsule including the first plating layer and the second plating layer.
 11. The method for manufacturing the latent heat storage material according to claim 10, wherein in the supporting the powder, the powder includes at least one of a metal powder formed of a same metal as the first plating layer and a metal oxide powder formed of an oxide of the same metal as the first plating layer.
 12. The method for manufacturing the latent heat storage material according to claim 11, wherein in the supporting the powder, the powder has a diameter from 1 micrometer to 100 micrometers.
 13. The method for manufacturing the latent heat storage material according to claim 10, wherein in the conducting the electroless plating, the latent heat storage member is held down so that an entirety of the latent heat storage member is positioned below a liquid surface of a plating liquid.
 14. The method for manufacturing the latent heat storage material according to claim 13, wherein in the conducting the electrolytic plating, the latent heat storage member having the first plating layer on the surface is held down so that an entirety of the first plating layer is positioned below a liquid surface of a plating liquid.
 15. The method for manufacturing the latent heat storage material according to claim 10, wherein in the preparing the grain of the latent heat storage member, the grain of the latent heat storage member is formed by supplying a droplet of the latent heat storage member in a cooling liquid and solidifying the droplet from outside. 